1. Field of the Invention
The present invention pertains to an apparatus for premixing additives and for feeding them into a polymer stream.
2. Summary of the Related Art
Methods for adding additives to a polymer stream are known in the art. In Chemiefasern/Textilindustrie, Vol. 88, No. 36, January 1986, pp. 24-29, a process for feeding additives into a stream of polymer melt is described in which a partial stream is taken from the unmodified main melt stream emerging from a final reactor or extruder. The partial stream is then passed through a twin-shaft extruder equipped with special kneading elements. The additives are supplied to the twin-shaft extruder by a continuous metering system and blended into the partial polymer melt stream. The partial stream containing the additives is then mixed back into the main melt stream, static mixing elements being used to achieve a uniform mixture.
DE 4,039,857 A1 discloses an apparatus for direct, continuous modification of polymer melts in which, again, a partial melt stream is taken from the main melt stream and re-directed to an extruder. The additives to be supplied arrive in the extruder via a feed pump. After the partial melt stream has been modified by the incorporation of the additives, it is returned to the main melt stream.
A process for feeding additives into a polymer melt stream is known from DE 198-41,376 A1, in which a partial stream is branched off from the polymer melt stream and divided into additional partial streams. These latter partial streams are directed to a planetary gear pump, to which at least one additive is also supplied. Then the partial streams are recombined and sent through a static mixer, from which it is returned to the main melt stream.
The disadvantage of known apparatuses and processes is that areas where the polymer melt can have undesirably long dwell times (and where it is possible for the polymer melt to form deposits) are created at the point where a portion of the polymer melt is branched off from the main melt stream and at the point where the polymer melt treated with additives is returned to the main melt stream. In addition, known apparatuses require a complicated apparatus.
The present invention provides an apparatus for premixing additives and for feeding them into a polymer melt stream, which apparatus allows short polymer melt residence times and requires only a relatively simple apparatus.